Ge-cr alloy sputtering target and process for producing the same

ABSTRACT

A Ge—Cr alloy sputtering target containing 5 to 50 at % of Cr and having a relative density of 95% or more, and a manufacturing method of such a Ge—Cr alloy sputtering target wherein Cr powder having a minus sieve of 75 μm or less, and Ge powder having a minus sieve of 250 μm or less and having a BET specific surface area of 0.4 m 2 /g or less are dispersively mixed in an even manner, and sintered thereafter. Thereby provided is a Ge—Cr alloy sputtering target capable of suppressing variation of the deposition speed and film composition, as well as improving the production yield, of the GeCrN layer deposited with reactive sputtering as the intermediate layer between the recording layer and protective layer of a phase-change optical disk, and the manufacturing method of such a target.

TECHNICAL FIELD

The present invention relates to a Ge—Cr alloy sputtering target capableof suppressing the deposition speed variation and the accompanyingcomposition deviation, and obtaining stable sputtering characteristicsupon forming a GeCrN thin film with reactive sputtering employing theGe—Cr alloy sputtering target, and the manufacturing method thereof.

BACKGROUND ART

In recent years, high density recordable optical disc technology capableof recording/reproduction without requiring a magnetic head has beendeveloped, and is rapidly attracting attention. This optical disc can beclassified into the three categories of read-only, write-once andrewritable. Particularly, the phase change method employed in thewrite-once or rewritable type discs is attracting attention.

This phase change optical disc performs the recording/reproduction ofinformation by heating and increasing the temperature of a recordingthin film on a substrate by irradiating a laser beam thereto, andgenerating a crystallographic phase change (amorphous→crystal) in thestructure of such recording thin film. More specifically, thereproduction of information is performed by detecting the change in thereflectivity caused by the change in the optical constant of the phase.

The aforementioned phase change is performed with the irradiation of alaser beam narrowed down to a diameter of approximately 1 to several μm.Here, for example, when a 1 μm laser beam passes through at a linearvelocity of 10 m/s, light is irradiated to a certain point on theoptical disc for 100 ns, and it is necessary to perform theaforementioned phase change and detect the reflectivity within such timeinterval.

Moreover, in order to realize the foregoing crystallographic phasechange, that is, the phase change between amorphous phase and crystal,not only will the phase change recording layer be subject to fusion andquenching more than once, the peripheral dielectric protective layer andaluminum alloy will also be repeatedly subject thereto.

In light of the above, a phase change optical disc has a four-layerstructure wherein both sides of the recording thin film layer of aGe—Sb—Te are sandwiched with protective layers of a zinc sulfide-siliconoxide (ZnS—SiO₂) high-melting point dielectric, and an aluminum alloyreflective layer is additionally provided thereto.

In the above-mentioned structure, demanded of an optical functioncapable of increasing the absorption in the amorphous portion andcrystal portion and giving a large reflectivity difference, also of afunction for giving the recording film the resistivity to moisture andpreventing the deformation caused by the heat of the recording thin filmas well as a function for controlling the thermal conditions uponrecording (c.f. “Kogaku” magazine, volume 26, no. 1, pages 9 to 15).

As described above, the protective layer of a high-melting pointdielectric must be durable against repeated thermal stress caused by theheating and cooling, must not allow such thermal effect to influence thereflective film or other areas, and it is also required to be thin, oflow reflectivity, and of strong resistivity against deterioration. Fromthis perspective, the dielectric protective layer plays an importantrole.

Generally speaking, although a phase change optical disk such as aDVD-RAM guarantees the number of rewritings 10⁵ to 10⁶ times, there areproblems of the rewriting characteristics deteriorating as a result of Sor the like diffusing from the zinc sulfide-silicon oxide (ZnS—SiO₂)layer used for protecting the foregoing recording layer.

As a method of overcoming this problem, an intermediate layer is beingprovided between the recording layer and protective layer, and, inparticular, GeCrN materials are being proposed as the material for suchintermediate layer.

Upon forming a GeCrN intermediate layer, a Ge—Cr alloy target isgenerally used, and reactive sputtering is performed in a nitrogen gasatmosphere.

Nevertheless, with a conventional target, there was deposition speedvariation, and there were problems in that such variation would triggerthe deviation of the film composition, which would result in defectiveproducts and deterioration of the production yield.

As conventional technology, disclosed is technology which uses Ge—Crmaterials and the like, and a compositional discontinuous faceorthogonal to the thickness direction is set, and the space between theupper face, which is the face on the side in which sputtering isstarted, and the compositional discontinuous face is defined as a firstregion. Moreover, for forming a thin film containing a plurality ofcomponents in a desired ratio from immediately after the start of use,the content of each component in the 1st region is set in such a mannerthat the lower is the sputtering rate of a component, the higher is itsconcentration as compared with the desired ratio of the formed thin film(c.f. Japanese Patent Laid-Open Publication No. 2000-178724).

Further, as a conventional Ge—Cr sputtering target, disclosed is asputtering target in which, when the X-ray diffraction intensity ismeasured with the sputtering target, the ratio of a peak intensity of(220) plane against a peak intensity of (111) plane, (I₂₂₀/I₁₁₁), is 0.3or more, and the spread of the peak-intensity ratio I₂₂₀/I₁₁₁ on thewhole target-surface is within ±30% (cf., for example, Japanese PatentLaid-Open Publication No. 2002-38258).

Moreover, as a conventional Ge—Cr sputtering target, disclosed is atarget in which the Ag content and the Au content in the high-purity Geor Ge alloy are each 5 ppm or below, and the variation of the Ag contentand Au content in the whole target are each within 30% (cf., forexample, Japanese Patent Laid-Open Publication No. 2002-69624).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a Ge—Cr alloysputtering target capable of suppressing the variation of the depositionspeed and film composition, as well as improving the production yield,of the GeCrN layer deposited by reactive sputtering as the intermediatelayer between the recording layer and protective layer of a phase-changeoptical disk, and the manufacturing method of such a target.

In order to achieve the foregoing object, as a result of intense study,the present inventors discovered that the variation of the depositionspeed and film composition can be suppressed and the production yieldcan be improved by optimizing the conditions of the target density, andthe variation of the density and composition.

Based on the foregoing discovery, the present invention provides:

1. A Ge—Cr alloy sputtering target containing 5 to 50 at % of Cr andhaving a relative density of 95% or more;

2. A Ge—Cr alloy sputtering target according to paragraph 1 above,wherein the relative density is 97% or more;

3. A Ge—Cr alloy sputtering target according to paragraph 1 or paragraph2 above, wherein the density variation in the target is within ±1.5%;

4. A Ge—Cr alloy sputtering target according to any one of paragraphs 1to 3 above, wherein the composition variation in the target is within±0.5%; and

5. A Ge—Cr alloy sputtering target according to any one of paragraphs 1to 4 above, wherein, in X-ray diffraction, the ratio B/A of the maximumpeak intensity A of Ge phase in a 2θ range of 20° to 30° and of themaximum peak intensity B of GeCr compound phase in a 2θ range of 30° to40° is 0.18 or more.

The present invention also provides:

6. A manufacturing method of a Ge—Cr alloy sputtering target, comprisingthe steps of evenly dispersing and mixing Cr powder of 75 μm or less andGe powder of 250 μm or less having a BET specific surface area of 0.4m²/g or less, and thereafter performing sintering thereto;

7. A manufacturing method of a Ge—Cr alloy sputtering target accordingto any one of paragraphs 1 to 5 above, comprising the steps of evenlydispersing and mixing Cr powder of 75 μm or less and Ge powder of 250 μmor less having a BET specific surface area of 0.4 m²/g or less, andthereafter performing sintering thereto.

8. A manufacturing method of a Ge—Cr alloy sputtering target accordingto paragraph 6 or paragraph 7 above, comprising the steps of evenlydispersing and mixing Ge powder having a BET specific surface area of0.1 to 0.4 m²/g, and thereafter performing sintering thereto; and

9. A manufacturing method of a Ge—Cr alloy sputtering target accordingto any one of paragraphs 6 to 8 above, wherein sintering is performedunder the conditions of hot pressing, a sintering temperature of 760 to900° C. and a surface pressure of 75 to 250 kg/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram (graph) showing the correlation of the specificsurface area of the Ge powder and the relative density (%) of the GeCrtarget. FIG. 2 is a diagram (graph) showing the correlation of the Crgrain size (minus sieve) and the relative density % of the GeCr target.

BEST MODE FOR CARRYING OUT THE INVENTION

The sputtering target of the present invention is characterized in thata Ge—Cr alloy sputtering target containing 5 to 50 at % of Cr has arelative density of 95% or more, and further a relative density of 97%or more.

This high density Ge—Cr alloy target can be manufactured by evenlydispersing and mixing Cr powder of 75 μm or less (hereinafter referredto as the “75 μm minus sieve” in this Description) and Ge powder of 250μm or less (hereinafter referred to as the “250 μm minus sieve” in thisDescription) having a BET specific surface area of 0.4 m²/g or less,preferably 0.3 m²/g or less, and thereafter performing sinteringthereto.

This kind of high density Ge—Cr alloy target suppresses the variation ofthe deposition speed and film composition of the GeCrN thin film formedby reactive sputtering, and significantly reduces the generation ofdefective products.

The GeCrN thin film formed as described above is extremely effective asan intermediate layer between the recording layer and protective layerof the phase change optical disk.

The relationship of the specific surface area of the Ge powder and therelative density (%) of the GeCr target is shown in FIG. 1. Further, therelationship of the Cr grain size and the relative density (%) of theGeCr target is shown in FIG. 2. These are correlation diagrams of thetarget when using the minus sieve of the respective powders.

Further, these are each of Ge-20 at % Cr and subject to hot pressingunder the conditions 800° C.×150 kg/cm².

If the relative density of the Ge—Cr alloy sputtering target is lessthan 95%, variation of the deposition speed and film composition willincrease, and the production yield will deteriorate.

Moreover, if Cr powder exceeding the 75 μm minus sieve and Ge powderexceeding the 250 μm minus sieve and exceeding the BET specific surfacearea of 0.4 m²/g are used for sintering, a relative density of 95% ormore cannot be attained, and, similarly, the variation of the depositionspeed and film composition will increase, and the production yield willdeteriorate.

Further, it is preferable that the density variation of the Ge—Cr alloysputtering target is within ±1.5%, and more preferable that thecomposition variation of the target is within ±0.5%. As a result, thevariation of the deposition speed and film composition can be furthersuppressed.

A GeCr compound phase and a Ge phase exist in the Ge—Cr alloy sputteringtarget, and it is desirable that, in the X-ray diffraction, the ratioB/A of the maximum peak intensity A of Ge phase in a 2θ range of 20° to30° and of the maximum peak intensity B of GeCr compound phase in a 2θrange of 30° to 40° is 0.18 or more. As a result, the uniformity can befurther improved.

Upon manufacturing a Ge—Cr alloy sputtering target, it is desirable toevenly disperse and mix Ge powder having a BET specific surface area of0.1 to 0.4 m²/g, and thereafter performing sintering thereto.

Moreover, upon performing such sintering, it is desirable that sinteringis performed by hot pressing under the conditions of a sinteringtemperature of 760 to 900° C. and a surface pressure of 75 to 250kg/cm².

As a result, Ge—Cr alloy sputtering target having a further stablerelative density of 95% or more can be manufactured thereby.

Since the increase in density of the sputtering target reduces pores andminiaturizes the crystal grains, and thereby makes the sputtering faceof the target even and smooth, a significant effect is yielded in thatthe formation of particles and nodules during sputtering can besuppressed and the target life can be prolonged.

EXAMPLES AND COMPARATIVE EXAMPLES

The present invention is now described with reference to the Examplesand Comparative Examples. These Examples are merely illustrative, andthe present invention shall in no way be limited thereby. In otherwords, the present invention shall only be limited by the scope of claimfor a patent, and shall include the various modifications other than theExamples of this invention.

Example 1

Ge powder having a purity of 5N (99.999%) and minus sieve of 100% m andCr powder having a purity of 3N (99.9%) and a minus sieve of 55 μm wereprepared, mixed so as to obtain Ge-20 at % Cr, and, filled in a carbondie after performing dry blending, and hot-pressed under the conditionsof a temperature of 800° C. and pressure of 150 kg/cm².

This sintered body was subject to finish processing to form a target.The relative density of the target was 99% (5.54 g/cm³ at 100% density).The density of samples arbitrarily extracted from three locations of thetarget was measured with the Archimedes method. The results are shown inTable 1.

Similarly, the composition of samples arbitrarily extracted from threelocations of the target was analyzed. The results are shown in Table 2.Further, the results of measuring the X-ray diffraction intensity areshown in Table 3 for the surface of the bulk sample cut from the target,said sample surface being faced against substrate.

Next, reactive sputtering was performed with this target under anitrogenous argon atmosphere (Ar:N₂=25:50 sccm) and power of 200 W, anda GeCrN film having a thickness of 300 Å was formed on a substrate. Themeasurement results of the variation of film thickness and permeabilityare shown in Table 4 and Table 5, respectively. TABLE 1 Densityvariation and XRD intensity Sample Density Example 1 99.0% 98.7% 99.4%Example 2 95.5% 96.0% 97.0% Example 3 98.8% 99.5% 99.2% ComparativeExample 1 88.0% 90.2% 92.0% Comparative Example 2 90.3% 95.2% 92.0%

TABLE 2 Variation in Composition Sample Composition Example 1 19.6%20.2% 19.8% Example 2 19.7% 20.4% 19.9% Example 3 50.2% 49.6% 50.2%Comparative Example 1 19.9% 18.9% 20.6% Comparative Example 2 19.7%21.5% 19.2%

TABLE 3 XRD intensity ratio Sample B/A Example 1 0.24 Example 2 0.31Comparative Example 1 0.10 Comparative Example 2 0.16

TABLE 4 Film Thickness (nm) Sample 1 2 3 4 5 6 7 8 9 Average σ Example 1290 325 295 315 330 310 285 290 290 303.3 17.0 Example 2 290 315 300 300325 310 280 305 285 301.1 14.5 Example 3 285 320 280 315 335 320 275 310290 303.3 21.2 Comparative Example 1 300 330 280 360 355 320 280 315 260311.1 34.3 Comparative Example 2 315 295 260 350 345 275 325 255 265298.3 36.8

TABLE 5 Permeability (%) 630 nm Sample A B C D Average σ Example 1 78.578.4 77.6 77.6 78.0 0.5 Example 2 79.0 78.8 78.2 77.9 78.5 0.5 Example 350.2 49.5 51.3 50.5 50.4 0.7 Comparative Example 1 79.2 73.2 74.3 84.177.7 5.0 Comparative Example 2 77.2 84.5 76.5 84.1 80.6 4.3

Example 2

Ge powder having a purity of 5N (99.999%) and minus sieve of 200 μm andCr powder having a purity of 3N (99.9%) and a minus sieve of 55 μm wereprepared, mixed so as to obtain Ge-20 at % Cr, filled in a carbon dieafter performing dry blending, and hot-pressed under the conditions of atemperature of 800° C. and pressure of 100 kg/cm².

This sintered body was subject to finish processing to form a target.The relative density of the target was 96% (5.54 g/cm³ at 100% density).The density of samples arbitrarily extracted from three locations of thetarget was measured with the Archimedes method. The results are shown inTable 1.

Similarly, the composition of samples arbitrarily extracted from threelocations of the target was analyzed. The results are shown in Table 2.Further, the results of measuring the X-ray diffraction intensity areshown in Table 3 for the surface of the bulk sample cut from the target,said sample surface being faced against substrate.

Next, reactive sputtering was performed with this target under anitrogenous argon atmosphere (Ar:N₂=25:50 sccm) and power of 200 W, anda GeCrN film having a thickness of 300 Å was formed on a substrate. Themeasurement results of the variation of film thickness and permeabilityare shown in Table 4 and Table 5, respectively.

Example 3

Ge powder having a purity of 5N (99.999%) and minus sieve of 75 μm andCr powder having a purity of 3N (99.9%) and a minus sieve of 25 μm wereprepared, mixed so as to obtain Ge-50 at % Cr, filled in a carbon dieafter performing dry blending, and hot-pressed under the conditions of atemperature of 800° C. and pressure of 150 kg/cm².

This sintered body was subject to finish processing to form a target.The relative density of the target was 97% (5.97 g/cm³ at 100% density).The density of samples arbitrarily extracted from three locations of thetarget was measured with the Archimedes method. The results are shown inTable 1.

Similarly, the composition of samples arbitrarily extracted from threelocations of the target was analyzed. The results are shown in Table 2.Further, the results of measuring the X-ray diffraction intensity areshown in Table 3 for the surface of the bulk sample cut from the target,said sample surface being faced against substrate.

Next, reactive sputtering was performed with this target under anitrogenous argon atmosphere (Ar:N₂=25:50 sccm) and power of 200 W, anda GeCrN film having a thickness of 300 Å was formed on a substrate. Themeasurement results of the variation of film thickness and permeabilityare shown in Table 4 and Table 5, respectively.

Comparative Example 1

Ge powder having a purity of 5N (99.999%) and minus sieve of 300 μm andCr powder having a purity of 3N (99.9%) and a minus sieve of 150 μm wereprepared, mixed so as to obtain Ge-20 at % Cr, filled in a carbon dieafter performing dry blending, and hot-pressed under the conditions of atemperature of 800° C. and pressure of 50 kg/cm².

This sintered body was subject to finish processing to form a target.The relative density of the target was 90% (5.54 g/cm³ at 100% density).The density of samples arbitrarily extracted from three locations of thetarget was measured with the Archimedes method. The results are shown inTable 1.

Similarly, the composition of samples arbitrarily extracted from threelocations of the target was analyzed. The results are shown in Table 2.Further, the results of measuring the X-ray diffraction intensity areshown in Table 3 for the surface of the bulk sample cut from the target,said sample surface being faced against substrate.

Next, reactive sputtering was performed with this target under anitrogenous argon atmosphere (Ar:N₂=25:50 sccm) and power of 200 W, anda GeCrN film having a thickness of 300 Å was formed on a substrate. Themeasurement results of the variation of film thickness and permeabilityare shown in Table 4 and Table 5, respectively.

Comparative Example 2

Ge powder having a purity of 5N (99.999%) and minus sieve of 350 μm andCr powder having a purity of 3N (99.9%) and a minus sieve of 75 μm wereprepared, mixed so as to obtain Ge-20 at % Cr, filled in a carbon dieafter performing dry blending, and hot pressed under the conditions of atemperature of 750° C. and pressure of 100 kg/cm².

This sintered body was subject to finish processing to form a target.The relative density of the target was 93% (5.54 g/cm³ at 100% density).The density of samples arbitrarily extracted from three locations of thetarget was measured with the Archimedes method. The results are shown inTable 1.

Similarly, the composition of samples arbitrarily extracted from threelocations of the target was analyzed. The results are shown in Table 2.Further, the results of measuring the X-ray diffraction intensity areshown in Table 3 for the surface of the bulk sample cut from the target,said sample surface being faced against substrate.

Next, reactive sputtering was performed with this target under anitrogenous argon atmosphere (Ar:N₂=25:50 sccm) and power of 200 W, anda GeCrN film having a thickness of 300 Å was formed on a substrate. Themeasurement results of the variation of film thickness and permeabilityare shown in Table 4 and Table 5, respectively.

As is evident from Examples 1 to 3 and Comparative Examples 1 and 2shown in Table 1, the relative density of Examples 1 to 3 was each 95%or more, and, with respect to Example 1 and Example 3, a relativedensity of 97% or more was attained. And in each of these cases, thedensity variation in the target was within ±1.5%.

Contrarily, the relative density of Comparative Example 1 andComparative Example 2 was less than 95%, and the density variation inthe target exceeded ±1.5%.

As shown in Table 2, the composition variation in the target of Examples1 to 3 was each within ±0.5%.

Contrarily, the composition variation in the target of ComparativeExample 1 and Comparative Example 2 exceeded ±0.5%.

Table 3 shows, for Examples 1 to 2 and Comparative Examples 1 and 2, theratio B/A of maximum peak intensity A of Ge phase in a 2θ range of 20°to 30° and the maximum peak intensity B of GeCr compound phase in a 2θrange of 30° to 40°. It is evident that Examples 1 to 2 satisfy thecondition of the present invention, i.e. 0.18 or more. However, withComparative Examples 1 and 2, B/A was less than 0.18.

The evaluation results of the variation of the film thickness andtransmittance for the target having the foregoing characteristics areshown in Table 4. It is evident that the variation of the film thicknessand transmittance in Examples 1 to 3 is significantly small. Contrarily,the variation of the film thickness and transmittance in ComparativeExamples 1 and 2 is significantly large, and is not suitable for atarget.

Moreover, the high density sputtering target of the present invention isable to suppress the formation of particles and nodules which take placeduring sputtering, and has an effect of improving the film thicknessuniformity. Contrarily, since the density was low in the targets ofComparative Examples 1 and 2, abnormal discharge occurred duringsputtering, and consequently there was a problem of increase in theformation of particles (dust) and nodules.

Accordingly, it is evident that the sputtering target of the presentinvention is extremely effective in forming a GeCrN layer deposited byreactive sputtering as the intermediate layer between the recordinglayer and protective layer of the phase change optical disk.

EFFECT OF THE INVENTION

When forming a GeCrN thin film by reactive sputtering employing the highdensity Ge—Cr alloy sputtering target of the present invention, thevariation of the deposition speed and the accompanying compositiondeviation can be effectively suppressed, and a superior effect isyielded in that stable sputtering characteristics can be obtained. As aresult, the incidence rate of defective products can be significantlyreduced. Further, upon sputtering, the generation of particles andnodules can be reduced, and the film thickness uniformity can also beimproved.

1. A Ge—Cr alloy sputtering target containing 5 to 50 at % of Crcharacterizing in that said target has a relative density of 97% ormore, that the density variation of said target is within ±1.5%, andthat, in X-ray diffraction, the ratio B/A of the maximum peak intensityA of Ge phase in a 2θ range of 20° to 30° and of the maximum peakintensity B of GeCr compound phase in a 2θ range of 30° to 40° is 0.18or more. 2-3. (canceled)
 4. Ge—Cr alloy sputtering target according toclaim 1, wherein the composition variation in the target is within±0.5%.
 5. (canceled)
 6. A manufacturing method of a Ge—Cr alloysputtering target, comprising the steps of evenly dispersing and mixingCr powder of 75 μm or less, and Ge powder of 250 μm or less and having aBET specific surface area of 0.1 to 0.4 m²/g, and thereafter performingsintering thereto. 7-9. (canceled)
 10. A method according to claim 6,wherein sintering is performed under the conditions of hot pressing at asintering temperature of 760 to 900° C. and a surface pressure of 75 to250 kg/cm².
 11. A method of manufacturing a Ge—Cr alloy sputteringtarget, comprising the steps of evenly dispersing and mixing Cr powderof 75 μm or less, and Ge powder of 250 μm or less having a BET specificsurface area of 0.1 to 0.4 m²/g, and thereafter performing sinteringthereto, wherein said sputtering target formed by the method contains 5to 50 at % of Cr, has a relative density of 97% or more and a densityvariation within ±1.5%, and has in X-ray diffraction a ratio B/A of amaximum peak intensity A of Ge phase in a 2θ range of 20° to 30° and ofa maximum peak intensity B of GeCr compound phase in a 2θ range of 30°to 40°, said ratio B/A being 0.18 or more.
 12. A method according toclaim 11, wherein sintering is performed under the conditions of hotpressing at a sintering temperature of 760 to 900° C. and a surfacepressure of 75 to 250 kg/cm².
 13. A method according to claim 12,wherein a composition variation in the target is within ±0.5%.
 14. Amethod according to claim 11, wherein a composition variation in thetarget is within ±0.5%.